Peristaltic pumps are well known and are used for various applications where a fluid is required to be pumped through a tube. Peristaltic pumps are able to control the flow rate of the fluid through the tube and can allow it to be dispensed in precise discrete volumes. Peristaltic pumps are considered advantageous as there is no contact between the fluid and the pump so contamination is avoided, back flow of liquids through the pump is inherently prevented and stripping and cleaning of the pump is not required--merely the quick and easy rinsing or exchanging of the tube.
There are two main types of known peristaltic pump. In the first the pumping action is achieved by compressing a flexible tube between rotating rollers and a fixed, profiled former. The fixed former is often semi-circular and the flexible tube is fixed so that it lies against the inside of the semi-circular shape. Rollers, usually two or three in number, are mounted on a rotating assembly concentric with the semi-circular former such that the tube is compressed by each roller in turn by the rotation of the assembly, which causes fluid trapped between two or more occlusions to be moved through the tube in the direction of rotation of the assembly. Such pumps require a considerable accuracy of manufacture to ensure that the correct clearances are maintained to completely occlude the tube without causing unnecessary deformation.
The second type of peristaltic pump, which is generally the one used for low duty applications, is where occlusion of the tube is achieved by stretching it over a rotating assembly consisting of three or four rollers. In this case it is the tension in the tube which causes the compression against the roller and thus the occlusion. This system, although much simpler in construction, has certain disadvantages. A fairly high tension is required to ensure occlusion of the tube and, since the tube is usually stretched only over one side of the roller assembly the tension causes appreciable side loading on the roller assembly, and its bearing shaft and associated motor, shortening the pump's useful life and increasing torque requirements.
The present invention overcomes or substantially mitigates the problems associated with known peristaltic pumps.